Incorporation of clay filler into synthetic rubber



Feb. 14, 1950 R. E. MEEKER'ETAL 2,497,464

INCORPORATION or CLAY FILLER INT0 sYRTrmTIc RUBBER RnedAprn 1s. 1947 www@ lhuejufal` Fell. .14, 195o rNcoaPoaA'rroN or CLAY man m'ro SYNTHETIC anneau Robert E. Hecken-South Charleston, W. Va., and

Harold J. E. Segrave, Washington, D. C., asaignors to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application April 19, 1947, Serial No. 742,498

16 Claims.

1 This invention relates to the incorporation of clay filler into synthetic rubber, and more particularly to improvements in the method of making synthetic rubber-clay master batches.

It has been suggested to incorporate clay illlers into synthetic rubber by incorporating the clay in the synthetic rubber latex and coagulating the mixture to give directly a so-called synthetic rubber-clay master batch. In prior practice, the clay has been added to a synthetic rubber latex such as a commercial GR-S synthetic rubber latex (aqueous emulsion polymerizate of a mixture of butadiene-1,3 and styrene) of 25-30% solids content in the form of an aqueous clay slurry of 15% maximum solids concentration, the mixture coagulated to large lterable flocs by conventional coagulation procedures, the ilocs illtered, and thel synthetic rubber-clay master batch dried. Large amounts of clay are lost in such prior processes by failure to be coagulated with the rubber fiocs, such clay particles remaining suspended in an unlterable condition in the mother liquor of the latex-coagulant mix. When amounts of clay were equal in weight to the synthetic rubber latex in such prior processes, los-ses of as high as 40 to 50% of the clay occurred. By the present invention, the clay retention is increased so that only small amounts of clay are lost, even at high ratios of clay to synthetic rubber.

We have found that if the synthetic rubber latex and clay mixture has a solids content of at least 40%, and this latex-clay mixture is introduced into an aqueous coagulant solution of polyvalent metal salt and/or strong acid, the coagulant content of which is maintained at a sufciently high concentration so that the coagulation of the latex-clay mix is almost instantaneous (to avoid dilution of the latex clay mix before coagulation), only very small amounts of clay will be lost, by failure toA be retained in the coagulum.

Commercial synthetic rubber latices as prepared for normal GR-S production have a solids content of about 25 to 35%. All percentages and parts referred to herein are by weight. With such latices, aqueous clay slurries of high clay content are necessary when added to such latices to give the 40% minimum solids content of the latex-clay mixture. Aqueous clay slurries become very viscous at around 15% solids concentration. Small amounts of sodium hydroxide, or mixtures of sodium hydroxide with sodium silicate or sodium phosphates, will readily give a low viscosity high solids suspension of clay in water which will readily mix with synthetic rubber latex of 30-35% solids content to give a latexclay mixture of the 40% minimum solids content. As little as 0.1% sodium hydroxide based on the clay will give a fluid aqueous clay slurry of 65-70% solids. Clay slurries of 5060% solids are generally suiicient to give the minimum latex-clay mixture solids concentration with conventional synthetic rubber latices. 'I'he clay, if desired, may be added directly to the latex in dry form, where a small amount of caustic soda is present in the latex.

The coagulant for the latex-clay mixture may be an aqueous solution of polyvalent metal salt, for example, aluminum sulfate, zinc sulfate, zinc chloride, magnesium sulfate, magnesium chloride, calcium chloride, or mixtures thereof, or an aqueous solution of strong acid, for example, sulfuric acid or hydrochloric acid. or a mixture of such acids, or a mixture of at least one such salt and at least one such strong acid. In such coagulant solutions, the amount of coagulant should be maintained at certain minimum concentrations of such polyvalent metal salt and/or strong acid coagulant. 'I'he minimum concentration of polyvalent metal salt or salts is 1% based on the aqueous phase or mother liquor of the latexcoagulant mixture. The minimum concentration of sulfuric acid (free H2504) is 0.5% based on the aqueous phase or mother liquor of the latexcoagulant mixture. In the case of hydrochloric acid in the coagulant, it is more convenient in practice to maintain a pI-l below 3 for the latexcoagulant mixture. We may, however, take the minimum concentration of hydrochloric acid (free HC1) as 0.1% based on the aqueous phase or mother liquor of the latex-coagulant mixture. As the salts are not appreciably used up in the coagulation of the latex-clay mixture, the amount of salt necessary to give the minimum concentration in the final mother liquor after coagulation may readily be calculated from the Water contents of the coagulating bath and latex to be added thereto. When sulfuric or hydrochloric acids are present in the coagulant solution, varying amounts of these may be used up depending on the alkalinity of the latex and the amount of alkali hydroxide, if any, used to disperse the clay, and provision therefor can be made in order to maintain the required minimum acid concentrations in the latex-coagulant mixture. As removal of large amounts of coagulant from the particles of coagulum is diincult, it is not recommended that the concentration in the coagulant bath of such polyvalent metal salts should be 3 maintained at over 4 percent, or of sulfuric acid over 2 percent, or of hydrochloric acid over 1 percent. Such coagulations may be made to take place at room or slightly elevated temperatures. It is preferred to carry out the acid coagulations at room temperature, e. g. 6080 F., whereas it is preferable to warm salt coagulant solutions somewhat, e. g. 120-l60 F. before coagulating the latex-clay mixture. We have found that the inclusion in the coagulant solution of a small amount of glue. .02% or more percent based on the weight of the coagulant solution will increase the clay retention. Higher amounts of glue are satisfactory but amounts over 0.1% based on the coagulant solution would not generally be used. This increase in clay retention by virtue of the glue addition has been found to amount to as much as 2 to 5% in the higher ratios of clay to synthetic rubber mixtures, e. s'. 90 to 110 parts of clay to 100 parts of synthetic rubber.

In the preparation of synthetic rubber latices, as is known, polymerizable monomeric compounds are emulsied in an aqueous medium' by means of an emulsifying agent, such as a water-soluble soap, and the polymerization is made to take place generally at elevated temperatur-es in the presence of a catalyst and other regulating materials. The monomeric compounds do not completely polymerlze and after the desired amount -of polymerization-has taken place, the unreacted monomers are removed from the synthetic rubber latex, as by venting oil' gaseous monomers and steam distilling liquid monomers. Examples oi' water-soluble soaps are the alkali-metal and ammonium salts of the soap-forming monocarboxylic acids, such as the alkali soaps of abietic acid and of aliphatic acids having chains of 8 to 24 carbon atoms in the molecule, for example, alkali soaps of caprylic, pelargonic, capric.

laurie, palmitic, stearic, oleic, linoleic acids. and

the like. 'I'he term alkali soaps is conventionally used herein as the generic term which includes alkali-metal and ammonium soaps, and is further used in its commonly accepted sense as exclusive of the alkali-earth and other polyvalent-metal water-insoluble soaps. Examples of polymerizable materials in the preparation of synthetic rubber latices are the various butadienes-1,3, for example, butadiene-1,3, methyl- 2-butadiene1,3 (isoprene), chloro-2-butadiene-- 1,3 (chloroprene) piperylene, 2,3-dimethyl-butadiene-1,3 and mixtures thereof. The polymerizable material as known maybe a mixture of one or more of such butadienes-LS with one or more other polymerizable compounds which are capable of forming rubbery copolymers with `nitriles and amides, such as acrylic acid. methyl acrylate, methyl methacrylate, acrylnnitrile, methacrylonitrile, methacrylamide; isobutylene; methyl vinyl ether; methyl vinyl ketone; Vinylidene chloride. Present day commercial synthetic vrubbers of the above types are polymerized chloro-2-butadiene-L3, known as neoprene kor GR-M rubber. copolymers of butadiene-1,3 and styrene, known as Buna B or GR-S rubber, and copolymers of butadiene-1,3 and acrylonitrile, known as Buna N or GR-A rubber.

The dispersing agents in the latex-clay mixture from the preparations of the synthetic rubber latex and the aqueous clay slurry should preferably be restricted to alkali-metal andl am monium (generally called alkali" as in conventional practicel soaps, hydroxides, silicates and phosphates, since the presence of other types oi dispersing agents, such as the commercial alkali sulfates and sulfonates of long chain organic compounds, (e. g. alkali alkyl sulfates, alkali alkylated-aryl suli'onates, alkali alkyl sulfosuccinates), tend to increase the loss of clay in the coagulation step when present in the latex-clay mixture.

The concentration of solids in the latex-clay mixture should be at least 40%. since excessive losses of clay are encountered when the solids concentration of the latex-clay mixture is below 40%, particularly where the ratio of clay to synthetic rubber is high,vas in the range 90 to 110 parts of clay per 100 parts of synthetic rubber. The ratio of clay to synthetic rubber in the latexclay mixture is not critical, and may be as low as parts of clay per 100 parts o1' synthetic rubber and as high as 110 to 150 parts of.clay per 100 parts of synthetic rubber. Higher concentrations of solids in the latex-clay mixture than 40% may be used, such higher concentrationsbeing dependent on the desired ratio of clay to latex solids and the concentration of the original synthetic rubber latex, since the clay mental efiect. This is illustrated in the accom-` panying drawing which is a graph showing the percent retention of clay in coagulated latex-clay .mixtures of equal parts of synthetic rubber and clay at various solids concentration of the latex-clay mixture from 29 to 47%. In the graph. the percent of charged clay retained on coagulation in an experimental series of runs is plotted against the total solids of the latexclay mixture. The synthetic rubber latex was prepared by the conventional aqueous emulsion polymerization of butadiene-1,3 and styrene in a 3:1 ratio emulsiiied with a sodium soap of a mixture of oleic, palmitic and stearic acids. 'The latex had a solids content of 30.8% Dry clay was added to the latex, to which a small amount of sodium hydroxide had been added, until the added clay weight was equal to the weight of the original latex solids. The latex-clay mixture was diluted in steps to about 29% solids. Samples of each concentration of the latex-clay mixture were coagulated by pouring into 1% aqueous H2804 (containing no glue) under constant slow agitation. All samples were coagulated with the same volume of coagulant and all were filtered and washed in the same manner so as to make the results comparable. Retentions were determined by recovering the clay not incorporated into the masterbatch. The percent clay retention in the various coagulations of the latex-clay mixtures of solids content from about 29% to 47% was determined. 'I'he graph is a typical curve, and shows that a minimum concentration of solids in the latex-clay mixture of is necessary to provide a reasonably high clay retention. The graph shows that it is not necessary that the concentration of the latex-clay mixture be greater than 43%, since at 4243% solids, the clay retention approaches the maximum, which is maintained with higher solids concentrations of the latex-clay mixture than 43%. The graph is intended to show the type of curve and the range of solid content of the latex-clay mixture for maximum clay retention, but the graph is not intended to show the absolute percent clay retention since the amount of clay retained in the maximum clay retention will vary with different runs.

The following examples are illustrative of our invention:

Example I distillation at reduced pressure. The conversion of monomers to synthetic rubber copolymer was about 79%. The solids content of the latex was about 32%.

A clay slurry was prepared by adding .1 part of sodium hydroxide to 40 parts of water and vigorously agitating while adding clay (at such a rate that it readily dispersed) to a total of parts of the clay. The clay slurry an-d latex were mixed in the proportion necessary to give a ratio of clay to latex solids of 105:100. The solids concentration of the latex-clay mixture was 42.1%. The mixture may be stored under a condition of mild agitation.

The latex-clay mixture was coagulated -by directing a stream of the same into a vessel containing aqueous hydrochloric acid in which the pH was maintained below 3 by the addition of small amounts of 0.35% aqueous hydrochloric acid as needed. The coagulant and aqueous hydrochloric acid additions contained about 0.02% glue based on the water phase thereof. The glue increases the clay retention 2 to 5%. Gentle but powerful agitation was maintained in the coagulating vessel. The temperature was maintained at about F. The coagulum product formed as ragged particles of suitable size for conventional GR-S nishing equipment. The coagulum particles were washed free of excess acid and uncombined clay, and dried, baled, and packaged similarly to GR-S synthetic rubber. The clay retention in the synthetic-rubber masterbatch was about 5% of the clay not being retained in the synthetic rubber-clay master batch.

Example II solution so that the glue concentration was about washed free of excess calcium chloride and uncombined clay, dewatered and dried, baled, and packaged similar to GR-S.

Example III Y It was desired to make a product containing parts of clay and 100 parts of GR-S synthetic rubber by the latex masterbatch process. The GR-S latex was made similarly to that in Examples I and II, and had a,32% solids content. A clay slurry was made conveniently in a vessel with vigorous agitation according to the following formula: clay (dry basis) 55 parts, sodium hydroxide 0.05 part, sodium silicate 0.6 part, water 45 parts. The sodium-hydroxide, and sodium silicate were added to the water, followed by the clay at such a rate that it is readily dispersed.

The latex and clay slurry were mixed by suitable equipment in the ratio of parts of dry clay per 100 parts of GR-S solids. The mixture could be stored under a condition of mild agitation. The solids concentration of the latex-clay mixture was 41 'I'he mixture was coagulated by admitting a stream of it into a vessel in which the concentration `of sulfuric acid was maintained at about 0.5 percent concentration. Suiiicient glue was added to the acid solution so'that the glue concentration was about 0.02 percent that that of the dilute acid used. Gentle, but powerful Vagitation was maintained in the coagulating vessel. The temperature was maintained at about 80 F. The product was lumpy; but oi suitable size for conventional GR-S finishing equipment. About 10 percent of the clay remained and was lost in the mother liquor. The product was washed free of excess acid and uncombined clay, and was dried, baled and packaged similarly to GRFS.

In view of the many changes and modiiications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for-an understanding of the scope of the protection afforded the invention.

Having thus described our invention. what we claim and desire to protect by Letters Patent ist 1. The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex and clay having a solids content of 40% ,to 43%, and having a dry clay to latex solids ratio from 502100 to 110:100, into a coagulant bath comprising an aqueous solution of sulfuric acid, the H2SO4 concentration of coagulant in the resulting mother liquor after the coagulation of the` synthetic rubber-clay mix being 0.5% to 2%.

2. The improvement in the method. of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex and clay having a solids content of 40% to 43%, and having a drv clay to latex solids ratio.

from 50t100'to 110:100, into a coagulant bath comprising an aqueous solution of'sulfuric acid,the

H2SO4 concentration of coagulant in the resultingv mother liquor after the coagulaton of the synthetc rubber-clay mix being 0.5% to 2%, said coagulant bath containing glue in amount from 0.02% to 0.1% o1' the aqueous coagulant solution used.

3. The improvement in the method of making a synthetic rubber-clay master batch whichcomprises directing a mixture of synthetic rubber latex and clay having a solids content of 40% to 43%. and having a dry clay to latex solids ratio from 50:100 to 110:100, into a coagulant bath comprising an aqueous solution of hydrochloric acid, the HC1 concentration of coagulant in the resulting mother liquor after the coagulation of the synthetic rubber-clay mix being 0.1% to 1%.

4. The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex and clay having a solids content of 40% to 43%, and having a dry clay to latex solids ratio from 501100 to 110:100, into a coagulant bath comprising an aqueous solution of hydrochloric acid, the HC1 concentration of coagulant in the resulting mother liquor after the coagulationv of the synthetic rubber-clay mix being 0.1% to 1%` said coagulant bath containing glue in amount from 0.02 to 0.1% of the aqueous coagulant solution used.

5. The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex and clay having a solids content of 40 to 43%, and having a dry clay to latex solids ratio from 50:100 to 110:100, into an aqueous solution of a coagulant selected from the group consisting of aluminum sulfate, zinc sulfate, zinc chloride, magnesium sulfate, magnesium chloride, calcium chloride, sulfuric acid, and hydrochloric acid, the coagulant content of the solution being maintained at a sufciently high concentration so that the coagulation of the latex-clay mix is almost instantaneous.

6. The improvement in the method of making asynthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex and clay having a solids content of 40 to 43%, and having a dry clay to latex solids ratio from 50:100 to 110:100, into an aqueous solution of a coagulant selected from the groupA consisting of aluminum sulfate, zinc sulfate, zinc chloride, magnesium sulfate, magnesium chloride, calcium chloride, sulfuric acid, and hydrochloric acid, the coagulant content of the solution being maintained at a suciently high concentration so that the coagulation of the latex-clay mix is almost instantaneous, said coagulant solution containing glue in amount from 0.02 to 0.1% of the aqueous coagulant solution used.

'7. The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex, comprising an aqueous emulsion polymerizate of a mixture of butadiene-1,3 with up to 70% of said mixture with butadiene-1,3 of styrene, and clay having a solids content of 40 to 43%, and having a dry clay to latex solids ratio from 50:100 to 110:100, into an aqueous solution of a coagulant selected from the group consisting of aluminum sulfate, zinc sulfate, zinc chloride, magnesium sulfate, magnesium chloride, calcium chloride, sulfuric acid, and hydrochloric acid, the lcoagulant content of the solution being maintained at a sufciently high concentration so that the coagulation of the latexclay mix is almost instantaneous.

8. The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a, mixture o1' synthetic rubber latex, comprising an aqueous emulsion polymerizate of a mixture of butadiene-1,3 with up to 70% of said mixture with butadiene-1,3 of styrene, and clay having a solids content of to 43%, and having a dry clay to latex solids ratio from 501100 to 110:100, into an aqueous solution of a coagulant selected from the group consisting of aluminum sulfate, zinc sulfate, zinc chloride, magnesium sulfate, magnesium chloride,

calcium chloride, sulfuric acid, and hydrochloric acid, the coagulant content of the solution being maintained at a sufliciently high concentration so that the coagulation of the latex-clay mix is almost instantaneous, said coagulant solution containing glue in amount from 0.02 to 0.1% of the aqueous coagulant solution used.

9.- The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex, comprising an aqueous emulsion polymerizate of a mixture of butadiene-1,3 with up to 70% of said mixture with butadiene-1,3 of a compound which contains a CH2=C group and is copolymerizable with butadiene-1,3 and clay having a solids content of 40 to 50%, and having a dry clay to latex solids ratio from :100 to 110:100, into a coagulant bath comprising an aqueous solution of calcium chloride, the amount of calcium chloride in said coagulant bath being equal to 1% to 4% of the mother liquor after the coagulation of the synthetic rubber-clay mix,

10. The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex, comprising an aqueous emulsion polymerizate of a mixture of butadiene-1,3 with up to of said mixture with butadiene-1,3 of a compound which contains a CH2=C group and is copolymerizable with butadiene-1,3, and clay having a solids content of 40 to 50%, and having a dry clay to latex solids ratio from 50:100 to 110:100, into a coagulant bath comprising an aqueous solution of glue and calcium chloride,

' the amount of glue being from 0.02 to 0.1% of said coagulant solution, and the amount of calcium chloride in said coagulant bath being equal to 1% to 4% of the mother liquor after the coagulation of the synthetic, rubber-clay mix.

l1. The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex, comprising an aqueous emulsion polymerizate of a mixture of butadiene-1,3 with up .f to r10% of said mixture with butadiene-1,3 of a compound which contains a CH2 =C group and is copolymerizable with butadiene-1,3, and clay having a solids content of 40 to 50%, and having a dry clay to latex solids ratio from 50:100 to 110:100, into a coagulant bath comprising an aqueous solution of sulfuric acid, the HzSOi concentration of which is maintained at from 0.5 to 2% during the coagulation operation.

12..The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of synthetic rubber latex, comprising an aqueous emulsion polymerizate of a mixture of butadiene-1,3 with up to 70% of said mixture with butadiene-1,3 of a compound which contains a CH2=C group and is copolymerizable with butadiene-1,3, and clay having a solids content of 40 to 50%, and having a. dry clay to latex solids ratio from 502100 to 110:100, into a coagulant bath comprising an aqueous solution containing glue and sulfuric compound which contains a CH=|=C group and is copolymerizable with butadiene-1,3. and clay having a solids'content of 40 to 50%, and hav ing a dry clay to latex solids ratio irom50:100

-to 110:100, into a coagulant bath comprising an l aqueous solution oi hydrochloric acid, the pH of which is maintained below 3 during the coagulation operation.

14. The improvement in the method of making a synthetic rubber-clay master batch which comprises directing a mixture of .synthetic rubber latex, comprising an aqueous emulsion polymerizate ci a mistura of butadiene-1,3 with up to '10% of said mixture with butadiene-1,3 oi' a compound which contains a CH2=C group and isl copolymerizable with butadiene-1,8. and clay having a sciids content of 40 to 50%. and havinga dry clay to latex solids ratio from 50:100 to 110:100. into a coagulant bath comprising an aqueous solution of hydrochloric acid, the HC1 concentration of which is maintained at from 0.1 to 1% during the coagulation operation.

15. The improvement in the method `of making a synthetic rubber-@icy master batch which comprises directing a mixture of synthetic rubber latex, comprising an aqueous emulsion poly,- merizate oi a mixture ci butadiene-1,3 with up to 70% o! said mixture with butadiene-1,8 oi a compound which contains a CHa==C group and is copolymerizahle with hutedieneni. and clay i0 having a solids content of to 50%, and having a dry clay to latex solids ratio from :100 to 110:100, into a coagulant bath comprising an aqueous solution oi' glue and hydrochloric acid,

the glue concentration oi which is 0.02 to 0.1%.

and the HC1 concentration of which is maintained at from 0.1 to 1% duringv the coagulation operation.

16. The improvement in the method. of mak-y ing a synthetic rubber-clay master batch whichv comprises directing a mixture of synthetic rubber latex, comprising an aqueous emulsion polymerizate of a mixture of butadiene-1,3 with upl to of said mixture with butadiene-1,3 of a compound which contains a CHz=C group and is copolymerizabiewith butadiene-1,3, and clay' having a solids content oi 40 to 50%, and having a dry clay to latex solids ratio from 50:100 to 110:100, into a coaguiant oath comprising an aqueous solution of glue and hydrochloric acid, the glue concentration of which is 0.02 to 0.1%.

- and the HC1. concentration oi which is maintained heiow a pH of il during the coagulation operation.

ROBERT E. MEEKER. HAROLD J; E. SEGRAVE.

earnestness @firm The following references are of record in the @TER Article by nor@ et sumo. and Eng. ehem., not. ieee. voi. se, no. io mages rois-101s). 

6. THE IMPROVEMENT IN THE METHOD OF MAKING A SYNTHETIC RUBBER-CLAY MASTER BATCH WHICH COMPRISES DIRECTING A MIXTURE OF SYNTHETIC RUBBER LATEX AND CLAY HAVING A SOLIDS CONTENT OF 40 TO 43%, AND HAVING A DRY TO LATEX SOLIDS RATIO FROM 40:100 TO 110:100, INTO AN AQUEOUS SOLUTION OF A COAGULANT SELECTED FROM THE GROUP CONSISTING OF ALUMINUM SULFATE, ZINC SULFATE CHLORIDE, MAGNESIUM SULFATE, MAGNESIUM CHLORIDE, CALCIUM CHLORIDE, SULFURIC ACID, AND HYDROCHLORIC ACID, THE COAGULANT CONTENT OF THE SOLUTION BEING MAINTAINED AT A SUFFICIENTLY HIGH CONCENTRATION SO THAT THE COAGULATION OF THE LATEX-CLAY MIX IS ALMOST INSTANTEOUS, SAID COAGULANT SOLUTION CONTAINING GLUE IN AMOUNT FROM 0.02 TO 0.1% OF THE AQUEOUS COAGULANT SOLUTION USED. 